Multiplexer, high-frequency front-end circuit, and communication device

ABSTRACT

A first filter of a multiplexer includes a ladder filter structure of acoustic wave resonators. An imaginary line obtained by connecting second ends of electrode fingers included in one comb-shaped electrode among a pair of comb-shaped electrodes of each resonator intersects a reference line that is a straight line extending in an acoustic wave propagation direction. When an angle defined by the reference line and the imaginary line of a first series resonator is represented by a first slant angle, an angle defined by the reference line and the imaginary line of a parallel resonator is represented by a second slant angle, and an angle defined by the reference line and the imaginary line of acoustic wave resonators is represented by a third slant angle, at least one of the first slant angle and the second slant angle is larger than the third slant angle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2017-192108 filed on Sep. 29, 2017 and is a ContinuationApplication of PCT Application No. PCT/JP2018/035558 filed on Sep. 26,2018. The entire contents of each application are hereby incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a multiplexer provided with a filterincluding acoustic wave resonators, a high-frequency front-end circuit,and a communication device.

2. Description of the Related Art

In recent years, to support a plurality of frequency bands and aplurality of wireless schemes, or multiband and multimode, using asingle terminal, multiplexers for separating (splitting) ahigh-frequency signal into individual frequency bands have been widelyused in communication devices such as mobile phone terminals. As afilter used in such a multiplexer, a filter device including acousticwave resonators has been proposed (see, for example, InternationalPublication 2015/098756). In this filter device, IDT (InterDigitalTransducer) electrodes of the acoustic wave resonators are arranged tobe slanted relative to an acoustic wave propagation direction tosuppress the transverse-mode ripple in the pass band of the filter.

However, the filter described in International Publication 2015/098756in which IDT electrodes are arranged to be slanted has a problem in thatspurious responses due to higher-order modes are likely to occur in afrequency band (stop band) higher than its pass band.

Such higher-order mode spurious responses are not characteristicallyproblematic in the pass band of the filter. In a multi-filterconfiguration in which paths extending through a plurality of filtersare interconnected, however, such higher-order mode spurious responsesmay affect the characteristics of another filter and causedeterioration. Specifically, if the frequency at which a higher-ordermode spurious response has occurred lies in the pass band of anotherfilter, the higher-order mode spurious response may cause an increase inthe ripple in the pass band (pass band ripple) of the other filter.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide multiplexers,high-frequency front-end circuits, and communication devices in each ofwhich a higher-order mode spurious response generated in the stop bandof a filter is able to be significantly reduced or prevented.

A multiplexer according to a preferred embodiment of the presentinvention includes a common terminal, a first terminal, and a secondterminal; a first filter provided on a first path electricallyconnecting the common terminal and the first terminal, the first filterincluding a plurality of acoustic wave resonators; and a second filterprovided on a second path electrically connecting the common terminaland the second terminal, the second filter having a pass band that ishigher in frequency than the first filter. The plurality of acousticwave resonators include two or more series resonators provided on thefirst path, and one or more parallel resonators each provided on a pathelectrically connecting a node on the first path and ground. A firstseries resonator that is closest to the common terminal among the two ormore series resonators is electrically connected to the common terminalwithout the one or more parallel resonators therebetween. Each of theplurality of acoustic wave resonators includes an IDT electrode definedby a pair of comb-shaped electrodes provided on a substrate havingpiezoelectricity. Each of the pair of comb-shaped electrodes of each ofthe plurality of acoustic wave resonators includes a plurality ofelectrode fingers that extend in a direction perpendicular orsubstantially perpendicular to an acoustic wave propagation direction,and a busbar electrode that connects first ends of the plurality ofelectrode fingers to each other. An imaginary line obtained byconnecting second ends of the plurality of electrode fingers included inone comb-shaped electrode among the pair of comb-shaped electrodesintersects a reference line that is a straight line extending in theacoustic wave propagation direction. When an angle defined by thereference line and the imaginary line of the first series resonator isrepresented by a first slant angle, an angle defined by the referenceline and the imaginary line of a first parallel resonator that isclosest to the common terminal among the one or more parallel resonatorsis represented by a second slant angle, and an angle defined by thereference line and the imaginary line of the rest of the plurality ofacoustic wave resonators is represented by a third slant angle, at leastone of the first slant angle and the second slant angle is larger thanthe third slant angle.

As described above, IDT electrodes are provided such that the imaginaryline described above and the reference line described above intersect,that is, IDT electrodes are slanted relative to the acoustic wavepropagation direction. This arrangement is able to significantly reduceor prevent generation of the transverse-mode ripple in each resonator.In addition, the IDT electrode of the series resonator that is theclosest to the common terminal is more slanted than the IDT electrodesof the rest of the plurality of other acoustic wave resonators. Thisarrangement is able to significantly reduce or prevent the higher-ordermode spurious response of the series resonator, which largely affectsthe second filter. With this configuration, it is possible tosignificantly reduce or prevent the higher-order mode spurious responsegenerated in the stop band of the first filter and to reduce theinsertion loss in the pass band of the second filter.

Further, at least one of the first slant angle and the second slantangle may be greater than or equal to about 2.5° and less than or equalto about 10°.

With this configuration, it is possible to further significantly reduceor prevent the higher-order mode spurious response generated in the stopband of the first filter.

Further, each of the first slant angle and the second slant angle may belarger than the third slant angle.

As described above, setting each of the first slant angle and the secondslant angle to be larger than the third slant angle is able tosignificantly reduce or prevent the higher-order mode spurious responsethat affects the second filter. With this configuration, it is possibleto significantly reduce or prevent the higher-order mode spuriousresponse generated in the stop band of the first filter and to reducethe insertion loss in the pass band of the second filter.

A multiplexer according to a preferred embodiment of the presentinvention includes a common terminal, a first terminal, and a secondterminal; a first filter provided on a first path electricallyconnecting the common terminal and the first terminal, the first filterincluding a plurality of acoustic wave resonators; and a second filterprovided on a second path electrically connecting the common terminaland the second terminal, the second filter having a pass band that ishigher in frequency than the first filter. The plurality of acousticwave resonators include one or more series resonators provided on thefirst path, and two or more parallel resonators provided on pathselectrically connecting the first path and ground. The two or moreparallel resonators include a first parallel resonator positioned on thecommon terminal side, and a parallel resonator positioned on the firstterminal side, as viewed from a first series resonator that is closestto the common terminal among the one or more series resonators. Each ofthe plurality of acoustic wave resonators includes an IDT electrodedefined by a pair of comb-shaped electrodes provided on a substratehaving piezoelectricity. Each of the pair of comb-shaped electrodes ofeach of the plurality of acoustic wave resonators includes a pluralityof electrode fingers that extend in a direction perpendicular orsubstantially perpendicular to an acoustic wave propagation direction,and a busbar electrode that connects first ends of the plurality ofelectrode fingers to each other. An imaginary line obtained byconnecting second ends of the plurality of electrode fingers included inone comb-shaped electrode among the pair of comb-shaped electrodesintersects a reference line that is a straight line extending in theacoustic wave propagation direction. When an angle defined by thereference line and the imaginary line of the first parallel resonator isrepresented by a first slant angle, an angle defined by the referenceline and the imaginary line of the first series resonator is representedby a second slant angle, and an angle defined by the reference line andthe imaginary line of the rest of the plurality of acoustic waveresonators is represented by a third slant angle, at least one of thefirst slant angle and the second slant angle is larger than the thirdslant angle.

As described above, IDT electrodes are provided such that the imaginaryline described above and the reference line described above intersect,that is, IDT electrodes are slanted. This arrangement is able tosignificantly reduce or prevent generation of the transverse-mode ripplein each resonator. In addition, the IDT electrode of the parallelresonator that is the closest to the common terminal is more slantedthan the IDT electrodes of the rest of the plurality of other acousticwave resonators. This arrangement is able to significantly reduce orprevent the higher-order mode spurious response of the parallelresonator, which largely affects the second filter. With thisconfiguration, it is possible to significantly reduce or prevent thehigher-order mode spurious response generated in the stop band of thefirst filter and to reduce the insertion loss in the pass band of thesecond filter.

Further, at least one of the first slant angle and the second slantangle may be greater than or equal to about 2.5° and less than or equalto about 10°.

With this configuration, it is possible to further significantly reduceor prevent the higher-order mode spurious response generated in the stopband of the first filter.

Further, each of the first slant angle and the second slant angle may belarger than the third slant angle.

As described above, setting each of the first slant angle and the secondslant angle to be larger than the third slant angle is able tosignificantly reduce or prevent the higher-order mode spurious responsethat affects the second filter. With this configuration, it is possibleto significantly reduce or prevent the higher-order mode spuriousresponse generated in the stop band of the first filter and to reducethe insertion loss in the pass band of the second filter.

Further, the substrate may include a piezoelectric layer having aprincipal surface on which the IDT electrodes are provided, ahigh-acoustic-velocity support substrate in which a bulk wave propagatesat a higher acoustic velocity than an acoustic velocity of an acousticwave that propagates in the piezoelectric layer, and alow-acoustic-velocity film that is provided between thehigh-acoustic-velocity support substrate and the piezoelectric layer andin which a bulk wave propagates at a lower acoustic velocity than anacoustic velocity of a bulk wave that propagates in the piezoelectriclayer.

With this configuration, the Q value of each resonator including an IDTelectrode provided on a substrate having a piezoelectric layer can bemaintained at a high value.

Further, a frequency of a higher-order mode spurious response generatedby the first filter may be included in the frequency pass band of thesecond filter.

With this configuration, it is possible to significantly reduce orprevent the higher-order mode spurious response generated in the stopband of the first filter and to reduce the insertion loss in the passband of the second filter.

Further, a high-frequency front-end circuit according to a preferredembodiment of the present invention includes a multiplexer according toa preferred embodiment of the present invention, and an amplifiercircuit electrically connected to the multiplexer.

With this configuration, it is possible to provide a high-frequencyfront-end circuit in which the higher-order mode spurious responsegenerated in the stop band of the first filter is able to besignificantly reduced or prevented and in which the insertion loss inthe pass band of the second filter can be reduced.

Further, a communication device according to a preferred embodiment ofthe present invention includes an RF signal processing circuit thatprocesses a high-frequency signal to be transmitted or received by anantenna element, and a high-frequency front-end circuit according to apreferred embodiment of the present invention, which transmits thehigh-frequency signal between the antenna element and the RF signalprocessing circuit.

With this configuration, it is possible to provide a communicationdevice in which the higher-order mode spurious response generated in thestop band of the first filter is able to be significantly reduced orprevented and in which the insertion loss in the pass band of the secondfilter can be reduced.

In the multiplexers and the like according to preferred embodiments ofthe present invention, it is possible to significantly reduce or preventthe higher-order mode spurious response generated in the stop band of afilter.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a basic configuration diagram of a multiplexer common topreferred embodiments of the present invention and a comparativeexample.

FIG. 2 is a circuit configuration diagram showing a first filter of themultiplexer according to the comparative example.

FIG. 3 is a diagram showing a higher-order mode spurious responsegenerated in the stop band of the first filter according to thecomparative example.

FIG. 4 is a diagram describing the return loss of the first filter inthe comparative example.

FIG. 5 is a circuit configuration diagram showing a first filter of themultiplexer according to Preferred Embodiment 1 of the presentinvention.

FIG. 6 includes a plan view and a cross-sectional view showing anacoustic wave resonator of the first filter according to PreferredEmbodiment 1 of the present invention.

FIG. 7A is a plan view of a series resonator that is the closest to acommon terminal in the first filter of Preferred Embodiment 1 of thepresent invention.

FIG. 7B is a plan view of a parallel resonator that is the closest tothe common terminal in the first filter of Preferred Embodiment 1 of thepresent invention.

FIG. 7C is a plan view of the other acoustic wave resonators in thefirst filter of Preferred Embodiment 1 of the present invention.

FIG. 8 is a diagram showing a change in the impedance of the acousticwave resonator according to Preferred Embodiment 1 of the presentinvention.

FIG. 9 is a diagram showing the relationships between frequency andphase for the acoustic wave resonator according to Preferred Embodiment1 of the present invention.

FIG. 10 is a diagram showing the relationship between a first slantangle of the acoustic wave resonator according to Preferred Embodiment 1of the present invention and the phase.

FIG. 11 is a circuit configuration diagram of a first filter accordingto Modification 1 of Preferred Embodiment 1 of the present invention.

FIG. 12 is a plan view of a parallel resonator that is the closest tothe common terminal in the first filter of Modification 1 of PreferredEmbodiment 1 of the present invention.

FIG. 13 is a circuit configuration diagram of a first filter accordingto Modification 2 of Preferred Embodiment 1 of the present invention.

FIG. 14 is a circuit configuration diagram of a first filter of themultiplexer according to Preferred Embodiment 2 of the presentinvention.

FIG. 15A is a plan view of a parallel resonator that is the closest tothe common terminal in the first filter of Preferred Embodiment 2 of thepresent invention.

FIG. 15B is a plan view of a series resonator that is the closest to thecommon terminal in the first filter of Preferred Embodiment 2 of thepresent invention.

FIG. 15C is a plan view of the other acoustic wave resonators in thefirst filter of Preferred Embodiment 2 of the present invention.

FIG. 16 is a circuit configuration diagram of a first filter accordingto Modification 1 of Preferred Embodiment 2. of the present invention.

FIG. 17 is a configuration diagram of a high-frequency front-end circuitaccording to Preferred Embodiment 3 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Background to Present Invention

First, the background to the present invention will be described withreference to FIG. 1 to FIG. 4. FIG. 1 is a basic configuration diagramof a multiplexer 1, which is common to both preferred embodiments of thepresent invention and a comparative example. In FIG. 1, an antennaelement 2 connected to a common terminal Port1 is also shown.

The multiplexer 1 includes the common terminal Port1, a first terminalPort11, a second terminal Port21, a first filter 11, and a second filter21. The first filter 11 is arranged on a first path r1 connecting thecommon terminal Port1 and the first terminal Port11. The second filter21 is arranged on a second path r2 connecting the common terminal Port1and the second terminal Port21. The pass band of the second filter 21 ishigher in frequency than that of the first filter 11.

FIG. 2 is a circuit configuration diagram showing the first filter 11 ofthe multiplexer 1 according to the comparative example.

The first filter 11 according to the comparative example is a ladderfilter including a plurality of acoustic wave resonators. The firstfilter 11 includes series resonators S1, S2, S3, S4, and S5, which areacoustic wave resonators arranged on the first path r1, and parallelresonators P1, P2, P3, and P4, which are acoustic wave resonatorsarranged on paths connecting the first path r1 and ground. The seriesresonators S1 to S5 are arranged in the stated order from the commonterminal Port1 toward the first terminal Port11. The parallel resonatorP1 is connected between the series resonators S1 and S2, the parallelresonator P2 is connected between the series resonators S2 and S3, theparallel resonator P3 is connected between the series resonators S3 andS4, and the parallel resonator P4 is connected between the seriesresonators S4 and S5. All or some of the series resonators S1 to S5 andthe parallel resonators P1 to P4 are hereinafter sometimes referred toas “resonators”.

A problem that can occur in the multiplexer 1 according to thecomparative example will be described with reference to FIG. 3. FIG. 3is a diagram showing a higher-order mode spurious response generated inthe stop band of the first filter 11 according to the comparativeexample. In FIG. 3, the thick line in the graph indicates an impedancecharacteristic of the series resonator S1 having a resonant frequency f1and an anti-resonant frequency f2, and the thin line in the graphindicates the insertion loss of the first filter 11 and the insertionloss of the second filter 21.

A higher-order mode spurious response appears as, for example, aripple-shaped impedance disturbance at frequencies higher than ananti-resonance point of a resonator. As shown in FIG. 3, if ahigher-order mode spurious response caused by any resonator of the firstfilter 11 occurs at a frequency f3, a portion of a signal of thefrequency f3 to be reflected by the first filter 11 is not reflected andis lost, and a pass band ripple appears in the second filter 21. Thepass band ripple causes insertion loss in the pass band of the secondfilter 21. To reduce the insertion loss of the second filter 21, thehigher-order mode spurious response caused by a resonator of the firstfilter 11 is to be significantly reduced or prevented.

As described above, arranging IDT electrodes of resonators to be slantedrelative to the acoustic wave propagation direction is able tosignificantly reduce or prevent the transverse-mode ripple in the passband of the first filter. However, when IDT electrodes are arranged tobe slanted, a higher-order mode spurious response is likely to occur.Accordingly, it is a challenge to suppress the higher-order modespurious response as much as possible while arranging IDT electrodes tobe slanted to significantly reduce or prevent the transverse-moderipple.

A description will now be given of, among the plurality of resonatorsincluded in the first filter 11, a resonator whose higher-order modespurious response more largely affects the second filter 21, that is, aresonator whose higher-order mode spurious response is significantlyreduced or prevented to effectively reduce the insertion loss of thesecond filter 21.

FIG. 4 is a diagram describing the return loss of the first filter 11 inthe comparative example. FIG. 4 is a diagram showing an increment ofreturn loss obtained when a predetermined frequency signal is input tothe first filter 11 in which a resistor is added to one of the pluralityof resonators, compared with the return loss obtained when apredetermined frequency signal is input to the first filter 11 from thecommon terminal Port1 side. The predetermined frequency signal to beinput to the first filter 11 is a signal including a frequency that liesin the stop band of the first filter 11 and that lies in the pass bandof the second filter 21.

The addition of a resistor to a resonator simulates the generation of ahigher-order mode spurious response in the resonator. The return loss ofthe first filter 11 increases by different amounts in accordance withthe resonator to which a resistor is added, that is, the resonator inwhich a higher-order mode spurious response is generated.

The return loss is the reflection loss of the first filter 11 seen fromthe common terminal Port1. The greater the return loss, the smaller thereflection of a signal by the first filter 11. That is, a frequencysignal in the pass band of the second filter 21 is absorbed by the firstfilter 11, and the insertion loss of the second filter 21 increases.

As shown in FIG. 4, the increment of return loss is at most about 0.7 dBwhen a resistor is added to the series resonator S1, which is theclosest to the common terminal Port1, and the increment of return lossis at most about 0.38 dB when a resistor is added to the second closestparallel resonator P1. In contrast, the increment of return loss is atmost about 0.05 dB when a resistor is added to the third closest seriesresonator S2, and the increment of return loss is approximately 0 dBwhen a resistor is added to each of the fourth and subsequent closestresonators P2 to P4 and S3 to S5, in which case the return loss isregarded as substantially not increasing. As described above, theincrease in the return loss of the first filter 11 is larger when ahigher-order mode spurious response is generated in a resonatorpositioned closer to the common terminal Port1, more specifically, theseries resonator and the parallel resonator in the initial stage on thecommon terminal Port1 side. Accordingly, to reduce the insertion loss ofthe second filter 21, it is effective to take measures to significantlyreduce or prevent the higher-order mode spurious response for the seriesresonator and the parallel resonator in the initial stage on the commonterminal Port1 side.

In the multiplexer 1 of this preferred embodiment, while each of theresonators included in the first filter 11 includes a structure thatsignificantly reduces or prevents a transverse-mode ripple, a resonatorpositioned close to the common terminal Port1 includes a structure thatsignificantly reduces or prevents a higher-order mode spurious response.This can reduce the insertion loss in the pass band of the second filter21.

The following describes preferred embodiments of the present inventionin detail with reference to examples and the drawings. All of thepreferred embodiments described below provide general or specificexamples. The values, shapes, materials, components, the arrangementsand connection forms of the components, and the like, which are providedin the following preferred embodiments, are examples and are notintended to limit the present invention. The components mentioned in thefollowing preferred embodiments are described as optional componentsunless they are specified in the independent claims. In addition, thecomponents shown in the drawings are not representative of exactproportions or dimensions. Additionally, in the drawings, substantiallythe same structural elements are denoted by the same numerals, and anyredundant description will be omitted or may be briefly given. In thefollowing preferred embodiments, the term “connected” includes directlyconnected and electrically connected via any other element and the like.

Preferred Embodiment 1

The multiplexer 1 according to Preferred Embodiment 1 of the presentinvention will be described with reference to FIG. 1 and FIG. 5 to FIG.10. Some components are redundant in Preferred Embodiment 1 and thecomparative example described above, and such redundant components willalso be described again in Preferred Embodiment 1.

1-1. Configuration of Multiplexer

The multiplexer 1 of Preferred Embodiment 1 is a multiplexer (splitter)including a plurality of filters having different pass bands, in whichantenna-side terminals of the plurality of filters are connectedtogether to a common terminal Port1. Specifically, as shown in FIG. 1,the multiplexer 1 includes the common terminal Port1, a first terminalPort11, a second terminal Port21, a first filter 11, and a second filter21.

The common terminal Port1 is common to the first filter 11 and thesecond filter 21 and is connected to the first filter 11 and the secondfilter 21 within the multiplexer 1. Further, the common terminal Port1is connected to an antenna element 2 outside the multiplexer 1. That is,the common terminal Port1 is also an antenna terminal of the multiplexer1.

The first terminal Port11 is connected to the first filter 11 within themultiplexer 1. The second terminal Port21 is connected to the secondfilter 21 within the multiplexer 1. The first terminal Port11 and thesecond terminal Port21 are connected to an RF signal processing circuit(RFIC: Radio Frequency Integrated Circuit, not shown) outside themultiplexer 1 via an amplifier circuit or the like (not shown).

The first filter 11 is arranged on a first path r1 connecting the commonterminal Port1 and the first terminal Port11. The first filter 11 is areceive filter whose pass band is, for example, the downlink frequencyband (receive band) in Band L (low band).

The second filter 21 is arranged on a second path r2 connecting thecommon terminal Port1 and the second terminal Port21. The second filter21 is a receive filter whose pass band is, for example, the downlinkfrequency band (receive band) in Band H (high band).

Preferable characteristics for the first filter 11 and the second filter21 are that the frequency bands (receive band or transmit band) in theircorresponding Bands are passed, while the other bands are attenuated. Inthe present preferred embodiment, the second filter 21 is set to have afrequency pass band higher than the first filter 11.

The first path r1 and the second path r2 are connected to each other ata node N. That is, the node N is a point at which the first path r1 andthe second path r2 are connected together. In the multiplexer 1, animpedance element, for example, an inductor for impedance matching maybe connected to the first path r1 connecting the first filter 11 and thenode N and to the second path r2 connecting the second filter 21 and thenode N, or to a path connecting the node N and the common terminalPort1, for example.

1-2. Configuration of Filter

Next, the configuration of the first filter 11 and the second filter 21will be described taking as an example the first filter 11 whose passband is the Band L.

FIG. 5 is a circuit diagram showing the first filter 11. As shown inFIG. 5, the first filter 11 includes acoustic wave resonators, namely,series resonators 111 s, 112 s, 113 s, and 114 s and parallel resonators111 p, 112 p, and 113 p. All or some of the series resonators 111 s to114 s and the parallel resonators 111 p to 113 p are hereinaftersometimes referred to as “resonators 110”.

The series resonators 111 s to 114 s are connected in series with eachother along the first path (series arm) r1 connecting the commonterminal Port1 and the first terminal Port11 in the stated order fromthe common terminal Port1 side. The parallel resonators 111 p to 113 pare provided on paths (parallel arms) connecting nodes n1, n2, and n3,each of which lies between adjacent ones of the series resonators 111 sto 114 s along the first path r1, and a reference terminal (ground) suchthat the parallel resonators 111 p to 113 p are connected in parallel toeach other. Specifically, the series resonator (first series resonator)111 s, which is the closest to the common terminal Port1, is connectedto the common terminal Port1 without the parallel resonators 111 p to113 p therebetween. The parallel resonator that is the closest to thecommon terminal Port1 among the parallel resonators 111 p to 113 p isthe parallel resonator (first parallel resonator) 111 p. A first end ofeach of the parallel resonators 111 p to 113 p is connected to any oneof the nodes n1, n2, and n3, and a second end thereof is connected tothe reference terminal.

As described above, the first filter 11 has a T-type ladder filterstructure defined by two or more series resonators (in this preferredembodiment, four series resonators, for example) arranged on the firstpath r1 and one or more parallel resonators (in this preferredembodiment, three parallel resonators, for example) each arranged on apath connecting the first path r1 and the reference terminal (ground).

The number of series resonators and the number of parallel resonators ofthe first filter 11 are not limited to four and three, respectively, andthe first filter 11 may include two or more series resonators and one ormore parallel resonators. The parallel resonator(s) may be connected tothe reference terminal via an inductor. Further, an impedance element,for example, an inductor and a capacitor may be added or connected to aseries arm or a parallel arm. While the parallel resonators areconnected to individual reference terminals in FIG. 5, individualreference terminals or a shared reference terminal may be selected inaccordance with, for example, the constraints of the mounting layout ofthe first filter 11.

1-3. Structure of Acoustic Wave Resonator

Next, the basic structure of the resonators 110 defining the firstfilter 11 will be described. The resonators 110 in this preferredembodiment are preferably surface acoustic wave (SAW) resonators, forexample.

The other filter, that is, the second filter 21, may not have theconfiguration described above and may be designed, for example, inaccordance with the predetermined filter characteristics and the like.Specifically, the second filter 21 may not have a ladder filterstructure, and may have, for example, a longitudinally-coupled filterstructure. Each of the resonators defining the second filter 21 is notlimited to a SAW resonator and may be a BAW (Bulk Acoustic Wave)resonator, for example. Alternatively, the second filter 21 may beprovided without using resonators and may be a LC resonant filter or adielectric filter, for example.

FIG. 6 includes a plan view and a cross-sectional view showing each ofthe resonators 110 of the first filter 11. The resonator 110 shown inFIG. 6 is used to describe a typical structure of the resonator 110described above, and the number and length of electrode fingers definingeach electrode are not limited to the shown ones.

As shown in the plan view in FIG. 6, the resonator 110 includes a pairof opposing comb-shaped electrodes 32 a and 32 b, and reflectors 32 carranged relative to the pair of comb-shaped electrodes 32 a and 32 b inan acoustic wave propagation direction D1. The pair of comb-shapedelectrodes 32 a and 32 b form an IDT electrode 32.

The comb-shaped electrode 32 a is defined by a plurality of parallelelectrode fingers 322 a arranged in comb rows, and a busbar electrode321 a that connects first ends e1 of the plurality of electrode fingers322 a to each other. The comb-shaped electrode 32 b is defined by aplurality of parallel electrode fingers 322 b arranged in comb rows, anda busbar electrode 321 b that connects first ends of the plurality ofelectrode fingers 322 b to each other. The pluralities of electrodefingers 322 a and 322 b extend in a direction perpendicular orsubstantially perpendicular to the acoustic wave propagation directionD1.

The reflectors 32 c, which are paired with each other, are arrangedrelative to the pair of comb-shaped electrodes 32 a and 32 b in theacoustic wave propagation direction D1. Specifically, the pair ofcomb-shaped electrodes 32 a and 32 b are disposed between the pair ofreflectors 32 c in the acoustic wave propagation direction D1. Each ofthe reflectors 32 c is defined by a plurality of parallel reflectionelectrode fingers and reflector busbar electrodes that connect theplurality of reflection electrode fingers to each other. In the pair ofreflectors 32 c, the reflector busbar electrodes are formed to extend inthe acoustic wave propagation direction D1.

An imaginary line L1 obtained by connecting second ends e2 of theplurality of electrode fingers 322 a (ends of the plurality of electrodefingers 322 a that are not connected to the busbar electrode 321 a) toeach other intersects a reference line L0, which is a straight lineextending in the acoustic wave propagation direction D1, at a slantangle α, which is a predetermined angle. Further, an imaginary line L1 aobtained by connecting the first ends e1 of the plurality of electrodefingers 322 a (ends of the plurality of electrode fingers 322 a that areconnected to the busbar electrode 321 a) to each other is parallel tothe imaginary line L1 and intersects the reference line L0 at the slantangle α. An imaginary line obtained by connecting second ends of theplurality of electrode fingers 322 b to each other and an imaginary lineobtained by connecting the first ends of the plurality of electrodefingers 322 b to each other also intersect the reference line L0 at theslant angle α. Accordingly, the individual IDT electrodes 32 definingthe resonators 110 are slanted IDTs in which the acoustic wavepropagation direction D1 intersects the direction in which thepluralities of electrode fingers 322 a and 322 b are arranged.

In a one-port resonator that includes a surface acoustic wave, thetransverse-mode ripple is generated between the resonant frequency andthe anti-resonant frequency and may deteriorate the transmissioncharacteristics in the pass band. To address the deterioration, thefirst filter 11 according to this preferred embodiment includes aslanted IDT as the IDT electrode 32 of the resonator 110. In the firstfilter 11 according to this preferred embodiment, furthermore, theseries resonators 111 s to 114 s and the parallel resonators 111 p to113 p have a structure described below to significantly reduce orprevent the higher-order mode spurious response described above.

FIG. 7A is a plan view showing the series resonator 111 s, which is theclosest to the common terminal Port1 in the first filter 11. FIG. 7B isa plan view showing the parallel resonator 111 p, which is the closestto the common terminal Port1 in the first filter 11. FIG. 7C is a planview showing the other acoustic wave resonators 112 s to 114 s, 112 p,and 113 p, different from the series resonator 111 s and the parallelresonator 111 p, in the first filter 11.

As shown in FIGS. 7A and 7B, in the first filter 11, the seriesresonator 111 s and the parallel resonator 111 p have different slantangles. As shown in FIGS. 7A and 7C, in the first filter 11, the seriesresonator 111 s has a different slant angle from the other acoustic waveresonators 112 s to 114 s, 112 p, and 113 p.

Specifically, as shown in FIG. 7A, the angle defined by the referenceline L0 and the imaginary line L1 of the series resonator 111 s isrepresented by a first slant angle α1, as shown in FIG. 7B, the angledefined by the reference line L0 and the imaginary line L1 of theparallel resonator 111 p is represented by a second slant angle α2, and,as shown in FIG. 7C, the angle defined by the reference line L0 and theimaginary line L1 of each of the acoustic wave resonators 112 s to 114s, 112 p, and 113 p is represented by a third slant angle α3. In thiscase, the relationship of the first slant angle α1>the second slantangle α2 and the first slant angle α1>the third slant angle α3 issatisfied. The first slant angle α1 is selected as appropriatepreferably from within a range greater than or equal to about 2.5° andless than or equal to about 10°, for example. The resonators 110defining the first filter 11 have the configuration described above,thus significantly reducing or preventing the higher-order mode spuriousresponse in the stop band of the first filter 11 while significantlyreducing or preventing generation of the transverse-mode ripple.

The respective third slant angles α3 of the acoustic wave resonators 112s to 114 s, 112 p, and 113 p may be the same or different.

1-4. Cross-Sectional Structure of Acoustic Wave Resonator

Referring back to FIG. 6, the cross-sectional structure of each of theresonators 110 will be described.

As shown in the cross-sectional view in FIG. 6, the IDT electrode 32,which is defined by the pluralities of electrode fingers 322 a and 322 band the busbar electrodes 321 a and 321 b, has a multilayer structure ofa close-contact layer 324 and a main electrode layer 325. Thecross-sectional structure of the reflectors 32 c is similar to thecross-sectional structure of the IDT electrode 32 and will not bedescribed hereinafter.

The close-contact layer 324 is a layer that enhances close contactbetween a piezoelectric layer 327 and the main electrode layer 325 andis preferably made of Ti, for example. The close-contact layer 324preferably has a film thickness of, for example, about 12 nm.

The main electrode layer 325 is preferably made of, for example, Alincluding about 1% Cu. The main electrode layer 325 preferably has afilm thickness of, for example, about 162 nm.

A protection layer 326 is provided on an outer surface of the IDTelectrode 32 and a substrate 320 and covers the IDT electrode 32 and thesubstrate 320. The protection layer 326 protects the main electrodelayer 325 from the external environment, adjusts thefrequency-temperature characteristic, improves moisture resistance, andother purposes and is a film preferably including, for example, silicondioxide as a main component. The protection layer 326 preferably has afilm thickness of, for example, about 25 nm.

The IDT electrode 32 and the reflectors 32 c having the configurationdescribed above are arranged on a principal surface of the substrate 320described below. The following describes a multilayer structure of thesubstrate 320 in this preferred embodiment.

As shown in the bottom portion of FIG. 6, the substrate 320 has astructure including a high-acoustic-velocity support substrate 329, alow-acoustic-velocity film 328, and the piezoelectric layer 327 suchthat the high-acoustic-velocity support substrate 329, thelow-acoustic-velocity film 328, and the piezoelectric layer 327 arestacked on one another in the stated order.

The piezoelectric layer 327 is a piezoelectric film having the IDTelectrode 32 and the reflectors 32 c arranged on a principal surfacethereof. The piezoelectric layer 327 is preferably made of, for example,a 50° Y-cut X-propagation LiTaO₃ piezoelectric single crystal orpiezoelectric ceramics (lithium tantalate single crystal cut along aplane whose normal lies along the axis rotated by about 50° from the Yaxis about the X axis or ceramics, with surface acoustic wavespropagating through the single crystal or ceramics along the X axis).The thickness of the piezoelectric layer 327 is preferably less than orequal to about 3.5λ, for example, where λ denotes the wave length of anacoustic wave determined by the electrode pitch of the IDT electrode 32,and is, for example, about 600 nm.

The high-acoustic-velocity support substrate 329 is a substrate thatsupports the low-acoustic-velocity film 328, the piezoelectric layer327, and the IDT electrode 32. The acoustic velocity of a bulk wave inthe high-acoustic-velocity support substrate 329 is higher than that ofa surface acoustic wave or a boundary acoustic wave propagating in thepiezoelectric layer 327, and functions to confine a surface acousticwave in a portion where the piezoelectric layer 327 and thelow-acoustic-velocity film 328 are stacked on each other and not topermit leakage downward from the high-acoustic-velocity supportsubstrate 329. The high-acoustic-velocity support substrate 329 ispreferably, for example, a silicon substrate having a thickness of, forexample, 125 μm.

The acoustic velocity of a bulk wave in the low-acoustic-velocity film328 is lower than the acoustic velocity of a bulk wave propagating inthe piezoelectric layer 327. The low-acoustic-velocity film 328 islocated between the piezoelectric layer 327 and thehigh-acoustic-velocity support substrate 329. Due to this structure andthe intrinsic properties of an acoustic wave whose energy isconcentrated in a low-acoustic-velocity medium, surface acoustic waveenergy is prevented from leaking outside the IDT electrode 32. Thelow-acoustic-velocity film 328 is a film preferably including, forexample, silicon dioxide as a main component. The thickness of thelow-acoustic-velocity film 328 is preferably less than or equal to about2λ, for example, where X denotes the wave length of an acoustic wavedetermined by the electrode pitch of the IDT electrode 32, and ispreferably, for example, about 670 nm.

In the multilayer structure of the substrate 320 in this preferredembodiment described above, the Q values at the resonant frequency andthe anti-resonant frequency can be significantly increased compared withthe structure of the related art in which, for example, a piezoelectricsubstrate is used as a single layer. In the multilayer structuredescribed above, however, due to the high efficiency of confinement ofacoustic wave energy in the thickness direction of the substrate 320,the higher-order mode spurious response generated by the resonator 110is less likely to attenuate and remains. In the resonator 110 of thispreferred embodiment having the multilayer structure described above,therefore, the higher-order mode spurious response is furthersignificantly reduced or prevented. In this preferred embodiment, asdescribed above, the series resonator 111 s, which is the closest to thecommon terminal Port1, has a larger slant angle than the other acousticwave resonators 112 s to 114 s and 111 p to 113 p, different from theseries resonator 111 s, and the higher-order mode spurious response ofthe first filter 11 can be significantly reduced or prevented.

1-5. Advantageous Effects, etc.

FIG. 8 is a diagram showing a change in the impedance of the acousticwave resonator 110 according to Preferred Embodiment 1. Specifically,FIG. 8 is a diagram showing the relationships between frequency andimpedance when the first slant angle α1 of the series resonator 111 schanges.

As shown in FIG. 8, in the series resonator 111 s, an impedancedisturbance occurs at a frequency of about 2990 MHz, which is in thestop band of the first filter 11, and a higher-order mode spuriousresponse appears. When observed for increments of the first slant angleα1, the impedance disturbance is large when the first slant angle α1 isequal to about 0°, with the impedance disturbance decreasing as thefirst slant angle α1 increases stepwise, for example, about 2.5°, about5°, about 7.5°, and about 10°. For example, when the first slant angleα1 is greater than or equal to about 2.5° and less than or equal toabout 10°, the impedance disturbance in the stop band of the firstfilter 11 is small, and the higher-order mode spurious responsedecreases.

FIG. 9 is a diagram showing the relationships between frequency andphase for the acoustic wave resonator 110, in which the impedance shownin FIG. 8 is converted into the phase using the S parameter. In theimpedance-to-phase conversion, differences in higher-order mode spuriousresponse when the first slant angle α1 changes appear markedly asdifferences in phase.

As shown in FIG. 9, in the series resonator 111 s, the phase increasesin the stop band of the first filter 11, and a higher-order modespurious response appears. When observed for increments of the firstslant angle α1, the phase is large when the first slant angle α1 isequal to about 0°, with the phase decreasing as the first slant angle α1increases stepwise. For example, when the first slant angle α1 isgreater than or equal to about 2.5° and less than or equal to about 10°,the phase in the stop band of the first filter 11 is small, and ahigher-order mode spurious response decreases. In FIG. 8 and FIG. 9, astop band response appears at a frequency of about 2700 MHz. The stopband response can be reduced by any other method.

FIG. 10 is a diagram showing the relationship between the first slantangle α1 of the acoustic wave resonator 110 and the phase. Specifically,in FIG. 10, the maximum value of the phase is plotted for increments ofthe first slant angle α1 on a graph whose horizontal axis represents thefirst slant angle α1 of the series resonator 111 s shown in FIG. 9 andwhose vertical axis represents phase.

As shown in FIG. 10, in the series resonator 111 s, the phase is largewhen the first slant angle α1 is equal to about 0°, and the phasebecomes small when the first slant angle α1 is greater than or equal toabout 2.5° and less than or equal to about 10°. As in FIGS. 8 to 10,setting the first slant angle α1 of the series resonator 111 s to begreater than or equal to about 2.5° and less than or equal to about 10°can make the impedance disturbance and the phase small and cansignificantly reduce or prevent generation of the higher-order modespurious response.

The multiplexer 1 according to this preferred embodiment includes thecommon terminal Port1, the first terminal Port11, the second terminalPort21, the first filter 11 arranged on the first path r1 connecting thecommon terminal Port1 and the first terminal Port11, the first filter 11including the plurality of acoustic wave resonators 111 s to 114 s and111 p to 113 p, and the second filter 21 arranged on the second path r2connecting the common terminal Port1 and the second terminal Port21, thesecond filter 21 having a pass band that is higher in frequency than thefirst filter 11. The plurality of acoustic wave resonators include twoor more series resonators (for example, the series resonators 111 s to114 s) arranged on the first path r1, and one or more parallelresonators (for example, the parallel resonators 111 p to 113 p) eacharranged on a path connecting one of the nodes n1 to n3 on the firstpath r1 and ground. The first series resonator 111 s, which is theclosest to the common terminal Port1 among the two or more seriesresonators 111 s to 114 s, is connected to the common terminal Port1without the parallel resonators 111 p to 113 p therebetween. Each of theplurality of acoustic wave resonators includes the IDT electrode 32,which is defined by the pair of comb-shaped electrodes 32 a and 32 bformed on the substrate 320 having piezoelectricity. Each of the pair ofcomb-shaped electrodes 32 a and 32 b of each of the plurality ofacoustic wave resonators includes the pluralities of electrode fingers322 a and 322 b that extend in a direction perpendicular orsubstantially perpendicular to the acoustic wave propagation directionD1, and the busbar electrodes 321 a and 321 b that connect first ends ofthe pluralities of electrode fingers 322 a and 322 b to each other. Theimaginary line L1 obtained by connecting the second ends e2 of theplurality of electrode fingers 322 a included in a comb-shaped electrode(for example, the comb-shaped electrode 32 a) among the pair ofcomb-shaped electrodes 32 a and 32 b to each other intersect thereference line L0, which is a straight line extending in the acousticwave propagation direction D1. When an angle defined by the referenceline L0 and the imaginary line L1 of the first series resonator 111 s isrepresented by the first slant angle α1, an angle defined by thereference line L0 and the imaginary line L1 of the first parallelresonator 111 p, which is the closest to the common terminal Port1 amongthe one or more parallel resonators 111 p to 113 p, is represented bythe second slant angle α2, and an angle defined by the reference line L0and the imaginary line L1 of the rest of the plurality of acoustic waveresonators 112 s to 114 s, 112 p, and 113 p is represented by the thirdslant angle α3, at least one of the first slant angle α1 and the secondslant angle α2 is larger than the third slant angle α3.

As described above, in each of the resonators 110 included in the firstfilter 11, the IDT electrode 32 is arranged such that the imaginary lineL1 and the reference line L0 intersect, that is, the IDT electrode 32 isslanted relative to the acoustic wave propagation direction D1. Thisarrangement can significantly reduce or prevent generation of thetransverse-mode ripple in each of the resonators 110. In addition, theIDT electrode 32 of the series resonator 111 s, which is the closest tothe common terminal Port1, is more slanted than the IDT electrodes 32 ofthe other acoustic wave resonators 112 s to 114 s and 111 p to 113 p.This arrangement can significantly reduce or prevent generation of thehigher-order mode spurious response of the series resonator 111 s, whichlargely affects the second filter 21. Therefore, it is possible tosignificantly reduce or prevent the higher-order mode spurious responseof the first filter 11 and to reduce the insertion loss in the pass bandof the second filter 21.

Modification 1 of Preferred Embodiment 1

In the multiplexer 1 according to Modification 1 of Preferred Embodiment1, the parallel resonator that is the closest to the common terminalPort1 among one or more parallel resonators has a larger slant anglethan the subsequent resonator(s).

FIG. 11 is a circuit configuration diagram of a first filter 11according to Modification 1 of Preferred Embodiment 1. The first filter11 according to Modification 1 includes a parallel resonator 111 a inplace of the parallel resonator 111 p provided in PreferredEmbodiment 1. The parallel resonator 111 a is positioned closest to thecommon terminal Port1 among the plurality of parallel resonators 111 a,112 p, and 113 p.

FIG. 12 is a plan view showing the parallel resonator 111 a, which isthe closest to the common terminal Port1 in the first filter 11 ofModification 1. In the first filter 11 of Modification 1, the parallelresonator 111 a has a different slant angle from the other parallelresonators 112 p and 113 p, different from the parallel resonator 111 a.

Specifically, as shown in FIG. 12, when the angle defined by thereference line L0 and the imaginary line L1 of the parallel resonator111 a is represented by a second slant angle α2, the relationship of thesecond slant angle α2>the third slant angle α3 is satisfied. The secondslant angle α2 is selected as appropriate preferably from within a rangegreater than or equal to about 2.5° and less than or equal to about 10°,for example. The second slant angle α2 may be the same or substantiallythe same angle as the first slant angle α1.

In the multiplexer 1 according to Modification 1 of Preferred Embodiment1, when the angle defined by the reference line L0 and the imaginaryline L1 of the parallel resonator 111 a, which is the closest to thecommon terminal Port1 among the one or more parallel resonators 111 a,112 p, and 113 p, is represented by a second slant angle α2, the secondslant angle α2 is larger than the third slant angle α3 described above.Among the parallel resonators 111 a, 112 p, and 113 p defining the firstfilter 11, the parallel resonator 111 a, which affects the second filter21, has the configuration described above, thereby further significantlyreducing or preventing the higher-order mode spurious response in thestop band of the first filter 11.

Modification 2 of Preferred Embodiment 1

In the multiplexer 1 according to Modification 2 of Preferred Embodiment1, the series resonator 111 s of the first filter 11 is defined byseparate resonators.

FIG. 13 is a circuit configuration diagram of a first filter 11according to Modification 2 of Preferred Embodiment 1. As shown in FIG.13, in the multiplexer 1 according to Modification 2, the seriesresonator 111 s of the first filter 11 is defined by two seriesresonators 111 b and 111 c, which are arranged in series. Among theseries resonators 111 b and 111 c, the series resonator 111 b, which isthe closest to the common terminal Port1, has the first slant angle α1.The series resonator 111 c positioned between the series resonator 111 band the node n1 also has the first slant angle α1.

In the multiplexer 1 according to Modification 2 of Preferred Embodiment1, the first slant angle α1 of the series resonators 111 b and 111 c ofthe series resonator 111 s, which is the closest to the common terminalPort1, is set to be larger than the third slant angle α3 of the acousticwave resonators 112 s to 114 s, 112 p, and 113 p positioned subsequentto the node n1. This can significantly reduce or prevent thehigher-order mode spurious response generated in the stop band of thefirst filter 11.

Preferred Embodiment 2

The multiplexer 1 of Preferred Embodiment 2 of the present inventionincludes a first filter 11A having a 7L-type ladder filter structure,which is different from the first filter of Preferred Embodiment 1having a T-type ladder filter structure.

FIG. 14 is a circuit configuration diagram of the first filter 11A ofthe multiplexer 1 according to Preferred Embodiment 2. As shown in FIG.14, the first filter 11A includes series resonators 111 s to 114 s andparallel resonators 111 d and 111 p to 113 p.

The series resonators 111 s to 114 s are provided on a first path(series arm) r1 connecting the common terminal Port1 and the firstterminal Port11 such that the series resonators 111 s to 114 s areconnected in series with each other in the stated order from the commonterminal Port1 side. The parallel resonators 111 d and 111 p to 113 pinclude the parallel resonator (first parallel resonator) 111 dpositioned on the common terminal Port1 side, and the parallelresonators 111 p to 113 p positioned on the first terminal Port11 side,as seen from the series resonator (first series resonator) 111 s, whichis the closest to the common terminal Port1 among the series resonators111 s to 114 s. The parallel resonator 111 d is connected to a path(parallel arm) connecting a node n0 between the common terminal Port1and the series resonator 111 s and the reference terminal (ground).Specifically, the parallel resonator 111 d, which is the closest to thecommon terminal Port1, is connected to the common terminal Port1 withoutthe series resonators 111 s to 114 s therebetween. The parallelresonators 111 p to 113 p are provided on paths connecting the nodes n1,n2, and n3, each of which lies between adjacent ones of the seriesresonators 111 s to 114 s along the first path r1, and the referenceterminal such that the parallel resonators 111 p to 113 p are connectedin parallel to each other.

Accordingly, the first filter 11A has a n-type ladder filter structuredefined by one or more series resonators (for example, the four seriesresonators 111 s to 114 s) arranged on the first path r1, and two ormore parallel resonators (for example, the four parallel resonators 111d and 111 p to 113 p) arranged on paths connecting the first path r1 andthe reference terminal.

FIG. 15A is a plan view showing the parallel resonator 111 d, which isthe closest to the common terminal Port1 in the first filter 11A. FIG.15B is a plan view showing the series resonator 111 s, which is theclosest to the common terminal Port1 in the first filter 11A. FIG. 15Cis a plan view showing the other acoustic wave resonators 112 s to 114 sand 111 p to 113 p, different from the parallel resonator 111 d and theseries resonator 111 s and, in the first filter 11A.

As shown in FIGS. 15A and 15B, in the first filter 11A, the parallelresonator 111 d and the series resonator 111 s have different slantangles. As shown in FIGS. 15A and 15C, in the first filter 11A, theparallel resonator 111 d has a different slant angle from the otheracoustic wave resonators 112 s to 114 s and 111 p to 113 p.

Specifically, as shown in FIG. 15A, the angle defined by the referenceline L0 and the imaginary line L1 of the parallel resonator 111 d isrepresented by a first slant angle α1, as shown in FIG. 15B, the angledefined by the reference line L0 and the imaginary line L1 of the seriesresonator 111 s is represented by a second slant angle α2, and, as shownin FIG. 15C, the angle defined by the reference line L0 and theimaginary line L1 of each of the other acoustic wave resonators 112 s to114 s and 111 p to 113 p is represented by a third slant angle α3. Inthis case, the relationship of the first slant angle α1>the second slantangle α2 and the first slant angle α1>the third slant angle α3 issatisfied. The first slant angle α1 is selected as appropriatepreferably from within a range greater than or equal to about 2.5° andless than or equal to about 10°, for example. The resonators 110defining the first filter 11A have the configuration described above,thereby significantly reducing or preventing the higher-order modespurious response generated in the stop band of the first filter 11Awhile significantly reducing or preventing generation of thetransverse-mode ripple.

The respective third slant angles α3 of the acoustic wave resonators 112s to 114 s and 111 p to 113 p may be the same or different.

In Preferred Embodiment 2 described above, only the parallel resonator111 d has the first slant angle α1, by way of example but notlimitation. The series resonator 111 s may also have a larger slantangle than the third slant angle α3.

That is, when the angle defined by the reference line L0 and theimaginary line L1 of the series resonator 111 s, which is the closest tothe common terminal Port1 among one or more series resonators (forexample, the series resonators 111 s to 114 s), is represented by asecond slant angle α2, the second slant angle α2 may be larger than thethird slant angle α3. The second slant angle α2 is selected asappropriate preferably from within a range greater than or equal toabout 2.5° and less than or equal to about 10°, for example. The secondslant angle α2 may be the same angle as the first slant angle α1. Theseries resonator 111 s, which is the closest to the common terminalPort1 among the series resonators 111 s to 114 s defining the firstfilter 11A of Preferred Embodiment 2, has the configuration describedabove, thereby further significantly reducing or preventing thehigher-order mode spurious response generated in the stop band of thefirst filter 11A.

(Modification 1 of Preferred Embodiment 2)

In the multiplexer 1 according to Modification 1 of Preferred Embodiment2, the parallel resonator 111 d of the first filter 11A is defined byseparate resonators.

FIG. 16 is a circuit configuration diagram of a first filter 11Aaccording to Modification 1 of Preferred Embodiment 2. As shown in FIG.16, the first filter 11A includes the series resonators 111 s to 114 sand the parallel resonators 111 d and 111 p to 113 p. The parallelresonator 111 d is defined by separate parallel resonators 111 e, 111 f,111 g, and 111 h.

The parallel resonators 111 e and 111 f are connected in series witheach other and are connected to a path connecting a node n0 between thecommon terminal Port1 and the series resonator 111 s and the referenceterminal. The parallel resonators 111 g and 111 h are connected inseries with each other and are connected to a path connecting a node n0between the common terminal Port1 and the series resonator 111 s and thereference terminal. Specifically, the parallel resonators 111 e and 111f, which are the closest to the common terminal Port1, are connected tothe node n0 without the series resonators 111 s to 114 s therebetween.The parallel resonators 111 g and 111 h, which are the second closest tothe common terminal Port1, are connected to the node n0 without theseries resonators 111 s to 114 s therebetween.

Accordingly, the first filter 11A has a n-type ladder filter structuredefined by one or more series resonators arranged on the first path r1and two or more parallel resonators (for example, the seven parallelresonators 111 e to 111 h and 111 p to 113 p) arranged on pathsconnecting the first path r1 and the reference terminal.

In Modification 1 of Preferred Embodiment 2, when the angle defined bythe reference line L0 and the imaginary line L1 of each of the parallelresonators 111 e to 111 h is represented by a first slant angle α1, andthe angle defined by the reference line L0 and the imaginary line L1 ofeach of the acoustic wave resonators 112 s to 114 s and 111 p to 113 pis represented by a third slant angle α3, the relationship of the firstslant angle α1>the third slant angle α3 is satisfied. The resonators 110defining the first filter 11A has the configuration described above,thereby significantly reducing or preventing the higher-order modespurious response generated in the stop band of the first filter 11A.

Preferred Embodiment 3

The multiplexer according to Preferred Embodiments 1 and 2 describedabove and their modifications can be applied to a high-frequencyfront-end circuit and further to a communication device including thehigh-frequency front-end circuit. In this preferred embodiment, thehigh-frequency front-end circuit and the communication device will bedescribed.

FIG. 17 is a configuration diagram of a high-frequency front-end circuit30 according to Preferred Embodiment 3. In FIG. 17, an antenna element2, an RF signal processing circuit (RFIC) 3, and a baseband signalprocessing circuit (BBIC) 4, which are connected to the high-frequencyfront-end circuit 30, are also shown. The high-frequency front-endcircuit 30, the RF signal processing circuit 3, and the baseband signalprocessing circuit 4 define a communication device 40.

The high-frequency front-end circuit 30 includes the multiplexer 1according to Preferred Embodiment 1, a receive-side switch 13, atransmit-side switch 23, a low-noise amplifier circuit 14, and a poweramplifier circuit 24.

The multiplexer 1 includes four filters. Specifically, the multiplexer 1includes a filter 12 and a filter 22 in addition to the first filter 11and the second filter 21. The filter 12 is a transmit filter whose passband is the uplink frequency band (transmit band) and is arranged on apath connecting the common terminal Port1 and an individual terminalPort12. The filter 22 is a transmit filter whose pass band is the uplinkfrequency band (transmit band) and is arranged on a path connecting thecommon terminal Port1 and an individual terminal Port22.

The receive-side switch 13 is a switch circuit including two selectionterminals individually connected to the first terminal Port11 and thesecond terminal Port21, which are output terminals of the multiplexer 1,and a common terminal connected to the low-noise amplifier circuit 14.

The transmit-side switch 23 is a switch circuit including two selectionterminals individually connected to the individual terminals Port12 andPort22, which are input terminals of the multiplexer 1, and a commonterminal connected to the power amplifier circuit 24.

The receive-side switch 13 and the transmit-side switch 23 are eachpreferably defined by, for example, a SPDT (Single Pole Double Throw)switch that connects the common terminal to a signal path correspondingto a predetermined band in accordance with a control signal from acontrol unit (not shown). The number of selection terminals to beconnected to the common terminal is not limited to one, and a pluralityof selection terminals may be connected to the common terminal. That is,the high-frequency front-end circuit 30 may support carrier aggregation.

The low-noise amplifier circuit 14 is a receive amplifier circuit thatamplifies a high-frequency signal (here, a high-frequency receivesignal) that has passed through the antenna element 2, the multiplexer1, and the receive-side switch 13 and outputs the amplified signal tothe RF signal processing circuit 3.

The power amplifier circuit 24 is a transmit amplifier circuit thatamplifies a high-frequency signal (here, a high-frequency transmitsignal) output from the RF signal processing circuit 3 and outputs theamplified signal to the antenna element 2 via the transmit-side switch23 and the multiplexer 1.

The RF signal processing circuit 3 performs signal processing, forexample, down-conversion, on a high-frequency receive signal input fromthe antenna element 2 via a receive signal path and outputs a receivesignal generated through the signal processing to the baseband signalprocessing circuit 4. Further, the RF signal processing circuit 3performs signal processing, for example, up-conversion, on a transmitsignal input from the baseband signal processing circuit 4 and outputs ahigh-frequency transmit signal generated through the signal processingto the power amplifier circuit 24. The RF signal processing circuit 3 isan RFIC, for example.

The signal processed by the baseband signal processing circuit 4 is, forexample, an image signal to be used to display an image, or an audiosignal to be used for the telephone conversation.

The high-frequency front-end circuit 30 may include any other circuitelement between the components described above.

The high-frequency front-end circuit 30 and the communication device 40having the configuration described above include the multiplexer 1according to Preferred Embodiment 1 described above. This cansignificantly reduce or prevent the higher-order mode spurious responsegenerated outside the pass band of the first filter 11 and reduce theinsertion loss in the pass band of the second filter 21.

The high-frequency front-end circuit 30 may include, in place of thefirst filter 11 of the multiplexer 1 according to Preferred Embodiment1, the first filter 11 of Modification 1 of Preferred Embodiment 1 orthe first filter 11A according to Preferred Embodiment 2 andModification 1 of Preferred Embodiment 2.

The communication device 40 may not include the baseband signalprocessing circuit 4 depending on the method for processing ahigh-frequency signal.

Other Preferred Embodiments

Multiplexers, high-frequency front-end circuits, and communicationdevices according to preferred embodiments of the present invention havebeen described with reference to preferred embodiments and theirmodifications. The present invention may be carried out in otherpreferred embodiments implemented by combining any of the components inthe preferred embodiments and modifications described above or inmodifications obtained by making various modifications conceived of by aperson skilled in the art to the preferred embodiments described abovewithout departing from the spirit of the present invention. Otherpreferred embodiments, modifications, and various devices including ahigh-frequency front-end circuit and a communication device according tothe present invention are also included in the present invention.

For example, Preferred Embodiment 3 described above describes amultiplexer including four filters, by way of example. However, thepresent invention is also applicable to, for example, a triplexer inwhich antenna terminals of three filters are shared, or a hexaplexer inwhich antenna terminals of six filters are shared. That is, themultiplexer preferably includes two or more filters.

Further, Preferred Embodiment 1 described above provides an example inwhich both the first filter and the second filter are receive filters.However, the present invention is applicable to a multiplexer in whichthe higher-order mode spurious response of a first filter lies in thepass band of a second filter, regardless of the use of the first andsecond filters and the like. Accordingly, at least one of the first andsecond filters may be a receive filter. The multiplexer may not have aconfiguration including both a transmit filter and a receive filter, andmay have a configuration including only a transmit filter or only areceive filter.

Further, Preferred Embodiment 1 described above provides a non-limitingexample in which each of the resonators 110 does not include offsetelectrode fingers (electrodes that protrude from busbar electrodes onopposite sides and face electrode fingers). Each resonator may includeoffset electrode fingers.

Further, the materials of the close-contact layer 324, the mainelectrode layer 325, and the protection layer 326 of the IDT electrode32 and the reflectors 32 c are not limited to the materials describedabove. In addition, the IDT electrode 32 may not have the multilayerstructure described above. The IDT electrode 32 may include a metal suchas Ti, Al, Cu, Pt, Au, Ag, or Pd or an alloy of these metals, forexample, or may be formed of a plurality of multilayer bodies includingsuch metals or alloys. The protection layer 326 may not be formed.

Further, in the substrate 320 of the acoustic wave resonator 110 ofPreferred Embodiment 1, the high-acoustic-velocity support substrate 329may have a structure in which a support substrate and ahigh-acoustic-velocity film in which a bulk wave propagates at a higheracoustic velocity than that of a surface acoustic wave or a boundaryacoustic wave that propagates in the piezoelectric layer 327 are stackedon each other.

Further, Preferred Embodiment 1 provides an example in which the IDTelectrodes 32 defining the first filter 11 are provided on the substrate320 having the piezoelectric layer 327. However, the substrate on whichthe IDT electrodes 32 are provided may be a piezoelectric substrateincluding the piezoelectric layer 327 as a single layer. In this case,the piezoelectric substrate is preferably made of, for example, a LiTaO₃piezoelectric single crystal or any other piezoelectric single crystalsuch as LiNbO₃. The substrate 320 on which the IDT electrodes 32 areprovided may use any suitable structure having piezoelectricity in whicha piezoelectric layer is stacked on top of a support substrate, otherthan a structure that is entirely formed of a piezoelectric layer.

Further, the piezoelectric layer 327 according to Preferred Embodiment 1described above includes a 50° Y-cut X-propagation LiTaO₃ singlecrystal. However, the cut angle of the single crystal material is notlimited to this. That is, the multilayer structure, the material, andthe thickness may be changed, for example, in accordance with thepredetermined bandpass characteristics and the like of the acoustic wavefilter device, and a surface acoustic wave filter that uses a LiTaO₃piezoelectric substrate having a different cut angle from that describedabove, a LiNbO₃ piezoelectric substrate, or the like can also achievesimilar advantageous effects.

Preferred embodiments of the present invention provide multiplexers,front-end circuits, and communication devices, which are each applicableto a multiband system, and can be widely used in communicationequipment, for example, mobile phones.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A multiplexer comprising: a common terminal, afirst terminal, and a second terminal; a first filter provided on afirst path electrically connecting the common terminal and the firstterminal, the first filter including a plurality of acoustic waveresonators; and a second filter provided on a second path electricallyconnecting the common terminal and the second terminal, the secondfilter having a pass band that is higher in frequency than the firstfilter; wherein the plurality of acoustic wave resonators include: twoor more series resonators provided on the first path; and one or moreparallel resonators each provided on a path electrically connecting afirst node on the first path and ground, a first series resonator thatis closest to the common terminal among the two or more seriesresonators is electrically connected to the common terminal without theone or more parallel resonators therebetween; each of the plurality ofacoustic wave resonators includes an interdigital transducer (IDT)electrode defined by a pair of comb-shaped electrodes provided on asubstrate having piezoelectricity; each of the pair of comb-shapedelectrodes of each of the plurality of acoustic wave resonatorsincludes: a plurality of electrode fingers that extend in a directionperpendicular or substantially perpendicular to an acoustic wavepropagation direction; and a busbar electrode that connects first endsof the plurality of electrode fingers to each other; an imaginary lineobtained by connecting second ends of the plurality of electrode fingersincluded in one comb-shaped electrode among the pair of comb-shapedelectrodes intersects a reference line that is a straight line extendingin the acoustic wave propagation direction; and when an angle defined bythe reference line and the imaginary line of the first series resonatoris represented by a first slant angle, an angle defined by the referenceline and the imaginary line of a first parallel resonator that isclosest to the common terminal among the one or more parallel resonatorsis represented by a second slant angle, and an angle defined by thereference line and the imaginary line of the rest of the plurality ofacoustic wave resonators is represented by a third slant angle, at leastone of the first slant angle and the second slant angle is larger thanthe third slant angle.
 2. The multiplexer according to claim 1, whereinat least one of the first slant angle and the second slant angle isgreater than or equal to about 2.5° and less than or equal to about 10°.3. The multiplexer according to claim 1, wherein each of the first slantangle and the second slant angle is larger than the third slant angle.4. The multiplexer according to claim 1, wherein the substrate includes:a piezoelectric layer including a principal surface on which the IDTelectrodes are provided, a high-acoustic-velocity support substrate inwhich a bulk wave propagates at a higher acoustic velocity than anacoustic velocity of an acoustic wave that propagates in thepiezoelectric layer; and a low-acoustic-velocity film that is providedbetween the high-acoustic-velocity support substrate and thepiezoelectric layer and in which a bulk wave propagates at a loweracoustic velocity than an acoustic velocity of a bulk wave thatpropagates in the piezoelectric layer.
 5. The multiplexer according toclaim 1, wherein a frequency of a higher-order mode spurious responsegenerated by the first filter is included in the frequency pass band ofthe second filter.
 6. A high-frequency front-end circuit comprising: themultiplexer according to claim 1; and an amplifier circuit electricallyconnected to the multiplexer.
 7. A communication device comprising: anRF signal processing circuit that processes a high-frequency signal tobe transmitted or received by an antenna element; and the high-frequencyfront-end circuit according to claim 6, the high-frequency front-endcircuit transmitting the high-frequency signal between the antennaelement and the RF signal processing circuit.
 8. The communicationdevice according to claim 7, wherein the antenna element is electricallyconnected to the common terminal.
 9. The multiplexer according to claim1, wherein the first path and the second path are electrically connectedto each other at a second node.
 10. The multiplexer according to claim1, wherein plurality of acoustic wave resonators includes three or moreseries resonators and two or more parallel resonators.
 11. Themultiplexer according to claim 1, wherein plurality of acoustic waveresonators includes four or more series resonators and three or moreparallel resonators.
 12. The multiplexer according to claim 1, whereineach of the plurality of acoustic wave resonators is a surface acousticwave (SAW) resonator or a bulk acoustic wave (BAW) resonator.
 13. Themultiplexer according to claim 4, wherein the IDT electrode includes aclose-contact layer and a main electrode layer, and the close-contactlayer is provided between the piezoelectric layer and main electrodelayer.
 14. A multiplexer comprising: a common terminal, a firstterminal, and a second terminal; a first filter provided on a first pathelectrically connecting the common terminal and the first terminal, thefirst filter including a plurality of acoustic wave resonators; and asecond filter provided on a second path electrically connecting thecommon terminal and the second terminal, the second filter having a passband that is higher in frequency than the first filter; wherein theplurality of acoustic wave resonators include: one or more seriesresonators provided on the first path; and two or more parallelresonators provided on paths electrically connecting the first path andground; the two or more parallel resonators include a first parallelresonator positioned on the common terminal side, and a parallelresonator positioned on the first terminal side, as viewed from a firstseries resonator that is closest to the common terminal among the one ormore series resonators; each of the plurality of acoustic waveresonators includes an interdigital transducer (IDT) electrode definedby a pair of comb-shaped electrodes provided on a substrate havingpiezoelectricity; each of the pair of comb-shaped electrodes of each ofthe plurality of acoustic wave resonators includes: a plurality ofelectrode fingers that extend in a direction perpendicular orsubstantially perpendicular to an acoustic wave propagation direction;and a busbar electrode that connects first ends of the plurality ofelectrode fingers to each other; an imaginary line obtained byconnecting second ends of the plurality of electrode fingers included inone comb-shaped electrode among the pair of comb-shaped electrodesintersects a reference line that is a straight line extending in theacoustic wave propagation direction; and when an angle defined by thereference line and the imaginary line of the first parallel resonator isrepresented by a first slant angle, an angle defined by the referenceline and the imaginary line of the first series resonator is representedby a second slant angle, and an angle defined by the reference line andthe imaginary line of the rest of the plurality of acoustic waveresonators is represented by a third slant angle, at least one of thefirst slant angle and the second slant angle is larger than the thirdslant angle.
 15. The multiplexer according to claim 14, wherein at leastone of the first slant angle and the second slant angle is greater thanor equal to about 2.5° and less than or equal to about 10°.
 16. Themultiplexer according to claim 14, wherein each of the first slant angleand the second slant angle is larger than the third slant angle.
 17. Ahigh-frequency front-end circuit comprising: the multiplexer accordingto claim 14; and an amplifier circuit electrically connected to themultiplexer.
 18. A communication device comprising: an RF signalprocessing circuit that processes a high-frequency signal to betransmitted or received by an antenna element; and the high-frequencyfront-end circuit according to claim 17, the high-frequency front-endcircuit transmitting the high-frequency signal between the antennaelement and the RF signal processing circuit.